[cpp-pistache-server] Fix missing semicolon in template and missing code to set default values of model schema

[shayan-eftekhari]

fix #10134
fix #10135

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@ravinikam @stkrwork @etherealjoy @MartinDelille @muttleyxd

[shayan-eftekhari]

Hello dear technical committee,

This is my first contribution to this project and I don't understand what caused the checks to fail. Would you please give me some hints and/or action points?

@ravinikam @stkrwork @etherealjoy @MartinDelille @muttleyxd

[wing328]

CI issues not related to this change.

[wing328]

LGTM. If no further question from anyone, I'll merge it over the weekend.